1. Field of the Invention
The present invention is broadly concerned with an improved fire retardant mastic composition particularly adapted for application to roofing decks, and which includes an additive therein causing the mastic to char and form a barrier to inhibit passage of flowable material therethrough, when the solidified mastic is subjected to temperatures of at least about 150.degree. C. In another aspect of the invention, complete roof constructions are provided including a metal deck, a layer of expanded synthetic resin foam atop the deck, with the fire retardant mastic of the invention applied to the deck and adhering the foam layer thereto. Also, a mastic material extruding apparatus for evenly spreading a flowable roof mastic is provided. Use of the invention permits fabrication of low cost replacement roofs which give a minimum of added dead load to an existing roof structure, while also imparting a high degree of thermal insulation and the ability to form a barrier resistant to passage of melted resin foam or other materials through the deck, in the event of a fire.
2. Description of the Prior Art
Many industrial-type buildings constructed during the last 30 to 40 years were roofed with metallic decking panels. Such panels were normally secured by screws, bolts, or rivets penetrating the metal decking, these penetrations being sealed. Metal roofs of this type suffer from a number of disadvantages, including a tendency to leak, and poor thermal insulation qualities. Over the years, as these metal roofs have begun to wear out, the building owners are faced with the task of providing a replacement roof. Generally speaking, it is a very expensive proposition to remove the original metal decking, and replace it with new decking. A replacement would typically cost approximately two times that of the modified insulated roof system concerned in this patent. Another alternative is to simply place a new metal deck atop the original deck. This is a problem inasmuch as the new metal roof imposes a significant dead load upon the structure of the building, which is particularly troublesome in the case of older buildings.
It has also been suggested in the past to provide a replacement built-up roof using the worn metal roof as a substrate. In such systems, preformed panels of expanded polystyrene, adapted to be placed over the contour of the original deck are employed. Such panels have rigid boards secured to the upper surfaces thereof, and are generally provided in 4'.times.4' or 4'.times.8' sections. With such built-up roofs, hot asphalt is initially applied to the decking, whereupon the preformed insulation panels are applied. At this point, a roofing membrane may be secured to the upper surface of the foam panels sections, followed by conventional lap joint sealing and finishing. In some of these prior built-up constructions, hot asphalt or existing mastics have been employed which include asphalt, mineral spirits, fibers and fillers. A problem with these roofs is that, in the event of a fire, the polystyrene foam readily melts and becomes flowable, and then drips into the building below with the asphalt. This can cause severe damage to the building and its contents, and indeed the fire insurance rates for a building having a built-up roof of this character are increased because of this hazard if insurable at all.
There is accordingly a real and unsatisfied need in the art for a new roofing system which can be used to form a safe built-up roof on an existing metal deck, while overcoming the problem of leak-through in the event of fire.